Suspension testing apparatus and method

ABSTRACT

In one aspect, the suspension testing apparatus uses air bearings (96) which have a low coefficient of friction. In a second aspect, the suspension testing apparatus ensures accurate measurement of suspension characteristics since the apparatus applies forces directly below the center of the vehicle wheel hub (12) (or forwardly or rearwardly therefrom at a distance equivalent to the pneumatic trail of the tire in the wheel (12)) to ensure that the point of application of force remains constant despite rotation of the support means (10) for the wheel (12) during deflection of the vehicle wheel (12). In a third aspect, the suspension testing apparatus provides new sensor means (22) for measuring the vehicle wheel deflection which uses a minimum number of transducers (162, 163, 164) to accurately monitor tire and wheel deflection during use. In a fourth aspect, the suspension testing apparatus uses mechanical actuators (15, 23) rather than hydraulic actuators to cause motion of the support means, which give an indication of the displacement of the support means. In a sixth aspect the suspension testing apparatus provides a method of testing a vehicle suspension using the suspension testing apparatus.

The present invention relates to apparatus for testing vehiclesuspensions and a method of doing so.

It is important to all vehicle manufacturers to know how the suspensionarrangements of their vehicles react under the forces experienced duringdriving, for instance forces arising during braking and acceleration andalso transverse loading during cornering.

Vehicle manufacturers are also keen to ascertain how the wheel isinclined relative to the vehicle body during movement of the vehiclesuspension under loading.

The present invention provides vehicle suspension testing apparatuscomprising: support means for supporting thereon a vehicle wheel or avehicle wheel hub, actuator means for applying a force to or fordisplacing the wheel support means, and sensor means for measuring theforce on and/or displacement of the vehicle wheel or the vehicle wheelhub, wherein the wheel support means comprises air bearing means whichin use raises the support means above the surface therebelow.

It has been found that the use of air bearing means is very signficant,since it is essential to allow the support means to move as freely aspossible under loading of the actuators without resistance to motion. Ifmechanical bearings are used then these tend to oppose n some degree themotion of the support means and this can lead to inaccuracies in themeasurements taken by the sensor means. This is of particular importanceif the vehicle being tested is a large commercial vehicle, when largefrictional forces can arise.

Preferably the support means has a flat lower exterior surface and theair bearing means comprises a plurality of individual air bearings eachattached to the flat lower exterior surface of the support means flyattachment means which allows limited motion of the air bearingsrelative to the support means and which comprises resilient means actingbetween the said lowermost surface of the support means and the airbearings.

The provision of the attachment means as mentioned above is importantsince it allows the alignment of the support means relative to itssupporting surface to ensure adequate lift at all parts of the supportmeans and to enable even load distribution across the support means.

The present invention also provides vehicle suspension testing apparatuscomprising: support means for supporting thereon a vehicle wheel or avehicle wheel hub, actuator means for applying a force to or fordisplacing the wheel support means, and sensor means for measuring theforces on and or displacement of the vehicle wheel or the vehicle hub,wherein the actuator means is connected to the wheel support means byconnection means either directly below the centre of the wheel hub or ata distance forwardly or rearwardly therefrom corresponding to thepneumatic trail or the tyre on the vehicle wheel, said connection meansallowing free pivotal motion of the wheel support means.

It is important to ensure that the forces applied by the actuatorsremain applied to a desired point so that during rotation of the tyreduring loading the point of loading does not alter such that arotational moment is applied to the support means which could lead toerroneous measurements or complicated calculations in obtaining correctmeasurements.

Preferably the support means comprises a wheel plate far receivingthereon a vehicle wheel and the connection means is connected to thesupport means directly underneath the centre of the wheel plate.

The present invention also provides vehicle suspension testing apparatuscomprising: support means for supporting thereon a vehicle wheel or avehicle wheel hub, actuator means for applying a force to or fordisplacing the wheel support means, and sensor means for measuring theforces on and/or displacement of the vehicle wheel or the vehicle wheelhub, wherein the sensor means comprises a frame fixed relative to thewheel or wheel hub, and a wishbone arrangement extending between theframe and a wheel clamp member for attachment to the vehicle wheel orwheel hub, rotation sensors being provided to measure the pivoting ofthe wishbone members relative to the frame and inclinometers beingprovided on the wheel clamp member to measure its inclination.

The present invention further provides vehicle suspension testingapparatus comprising: support means for supporting thereon a vehiclewheel or a vehicle wheel hub, actuator means for applying a force toand/or tar displacing the wheel support means and sensor means formeasuring the forces on and/or displacement of the vehicle wheel or thevehicle wheel hub, wherein the actuator means comprises a firstmechanical actuator for moving the support means in a directionlongitudinally along the vehicle and a second mechanical actuator formoving the support means transversely of the vehicle, which first andsecond mechanical actuators are respectively adapted to provideindications of the longitudinal and transverse displacement of thesupport means.

Mechanical actuators are advantageously used in preference to hydraulicactuators for several reasons. First, mechanical actuators tend to bevery accurate and precise actuators of low cost. Equivalent hydraulicactuators are very expensive and precise displacement of the supportmeans can only be achieved using complicating control and valvingsystems.

The mechanical actuators of the invention also provide an indication ofthe displacement of the support means, whereas electrical measurementapparatus will typically have to be used with hydraulic actuators todetermine displacement of the support means.

Preferably the actuator means comprises additionally a third mechanicalactuator for moving the support means vertically, which mechanicalactuator is adapted to provide an indication of the verticaldisplacement of the support means.

It is far safer to use a mechanical actuator to provide verticaldisplacement than a hydraulic actuator. On failure of the means poweringthe mechanical actuator the mechanical actuator will remain in itsextended position, whilst most forms of hydraulic actuator will not belocked in position. This is an important consideration when a heavyvehicle is being supported by the actuator, since use of hydraulicactuators can be very hazardous if on failure they do not support theweight of the vehicle and the support means is allowed to move under theweight of the vehicle.

In the preferred embodiments of the invention the mechanical actuatorsare ball and screw type actuators. These actuators provide a cheap,simple precise and efficient means of actuation.

Preferably the ball and screw type actuators of the invention arecoupled to electric motors which cause the actuators to move the supportmeans. As mentioned above, the arrangement is inherently safe since aball and screw actuator will not move under the weight of the vehicle ifthe electric motor powering it fails.

Preferably the vehicle suspension testing apparatus of the inventionadditionally comprises a frame on which are mounted the support meansand the actuator means, said actuator means acting between the frame andthe support means, said frame having clamping means for securing theframe to the body of the vehicle being tested.

Preferably the actuator means can apply a force on the wheel or wheelhub longitudinally and transversely at the vehicle.

Preferably the actuator means can also apply vertical forces on thewheel or wheel hub.

Preferably the support means comprises a wheel plate for receivingthereon a vehicle wheel and a bearing mounting plate located parallel toand vertically spaced below the wheel plate to which air bearings areattached, the actuator means extending between the wheel plate and thebearing mounting plate to attachment means which attaches the actuatormeans to the wheel plate and the bearing mounting plate respectivelybelow and above the centres of the plates, the attachment means allowingpivotal motion of the plates whilst restraining translational motion.

The invention further provides a method of testing a vehicle suspensionsystem including the steps of:

locating a wheel or wheel hub of a vehicle on the support means ofvehicle suspension testing apparatus as claimed in any one of thepreceding claims,

attaching the sensor means to the vehicle wheel or wheel hub,

applying a force to or displacing the support means using the actuatormeans,

measuring the displacement of the wheel or wheel hub using the sensormeans.

The present invention will now be described with reference to theaccompanying drawings in which;

FIG. 1 shows a first embodiment of the testing apparatus of theinvention

FIG. 2 shows a second embodiment of the testing apparatus of theinvention

FIG. 3 shows a third embodiment of the testing apparatus of theinvention

FIG. 4 shows in cross-section a detail of part of a preferred embodimentof the invention, showing the construction of the support means of theembodiment.

FIG. 5 shows a plan view of the support means shown in crosssection inFIG. 4

FIG. 6 shows an elevational view of part of an air bearing as used inthe support means of preferred embodiments of the invention shownpreviously in the embodiments of FIGS. 4 and 5

FIG. 7 shows a plan view of the air bearing of FIG. 6

FIG. 8 shows an elevational view of the air bearing of FIG. 6 and

FIG. 9 shows a cross-section of an elevational view of the attachmentmeans for attaching the actuator means to the support means in apreferred embodiment of the invention.

FIG. 10 shows a cutaway plan view of the support means of a preferredembodiment of the invention

FIG. 11 shows transducer apparatus according to a preferred embodimentof the invention

FIG. 12 shows schematically a commercial passenger vehicle arranged onthe suspension testing apparatus of one embodiment of the invention

FIG. 13 is an elevational view of the passenger vehicle shown in FIG. 11supported on the vehicle suspension testing apparatus of the invention

FIG. 14 shows a modification of the embodiment of FIG. 3.

Referring to FIG. 1 a preferred embodiment of the invention can be seento comprise the following elements; support means 10 and 11 forsupporting vehicle wheels (shown schematically at 12 and 13) andactuator means provided to cause movement of the support means (two ofthese are shown at 23 and 15).

The support means 10 and 11 each comprise a plurality of parallel plates24 and 25 spaced apart by spacers 26. The upper plate 24 is a wheelplate for supporting the vehicle wheel. The lower plate 25 is a bearingmounting plate. Under this plate three air bearings are attached.Examples of air bearings are described later with reference to FIGS. 6,7 and 8. It is preferable to use three air bearings since this ensureseven distribution of loading.

The support means 10 and 11 and the actuator means are located on frames16, 17 and 18. The frame 16 is attached to the frame 17 but isreleasably secured thereto so that the frame 16 can be moved relative tothe frame 17 to position a force transducer in member 14 in alignmentwith the support means.

The actuator 15 is of the mechanical ball screw type and acts betweeneither tile frame 17 or the surface below the frame 17 and the bottom ofthe support means 10. The actuator 15 is controlled by an electric motor19.

The frame 16 is a lateral loading frame and comprises two parts 27 and28. Part 28 is pivotally mounted on part 27. A member 14 which includesa force transducer is connected between the upper portion of the part 28and the support means 10. A mechanical actuator 23 is connected betweenthe frame part 27 and the frame part 28 and can be used to apply forceto and/or pivot the frame part 28, thereby causing member 14 to apply aforce to and/or displace the support means 10.

Similar provision is made for the wheel 13, although the components arenot shown.

A locking frame 20 is provided to secure the vehicle chassis relative tothe frames 18 and 17.

Various transducers are provided to measure forces on and movement ofthe wheels 12 and 13. The transducers for the wheel 2 can be seen. Theyinclude a vertical force transducer 21 and an arrangement 22 formeasuring the wheel position. The wheel position transducer apparatus 22will be described later in more detail with reference to a furtherfigure.

The second embodiment of the invention can be seen in FIG. 2 where wheelsupport means 30 and 31 are provided for the wheels 32 and 33.

In this embodiment the support means 30 and 31 are located respectivelyon frames 34 and 35. Frame 34 is shown in detail in the figure whileframe 35 is only shown schematically. Both frames are identical to oneanother and therefore only frame 34 will be described in detail.

The frame 34 comprises a base member 36 on which are mounted foursubframes 37. Each of the subframes has two sets of roller bearings 38.The roller bearings 38 locate in position a support member 39 which issecured to the bottom of the support means 30. A vertical actuator 40 isprovided beneath the support member 39 to control the vertical positionof the support member 39. The vertical actuator comprises a ball screwmechanical type actuator powered by an electric motor (not shown). Theroller bearings 33 allow movement of the support member, 39 relative tothe base 36 in a vertical direction only.

At the top of the support member 39 there are provided two arms 41 and42 which are located beneath the support means 30 and which haveupwardly directed flanges 43 and 44 at their ends.

Acting between the upright flanges 44 and 43 and the support means 30are two actuators 45 and 46. Both actuators are of the mechanical ballscrew type. Both actuators preferably include force transducers formeasuring the applied force.

The actuator 45 can be used to apply a force on the wheel 32 in adirection along the length of the vehicle and the actuator 46 can beused to apply a force on the wheel 22 in a direction transversely of thevehicle being tested. The exact arrangement of the wheel support means30 will be described hereafter in greater detail with reference to FIG.4.

Transducer apparatus 47 is provided to measure the movement of the wheel32.

The two frames 34 and 35 are both mounted on two transverse members 48and 49. The two frames 34 and 35 can be moved relative to each otheralong the transverse members 45 to 49 so that the testing apparatus canbe easily adjusted to test vehicles of different tracks.

Midway between the two frames 34 and 35 is provided a vertical frame 50which comprises two upright members 51 and 52 joined by an I-beam 53. Onthe I-beam in provided a clasping umber 54 which can be moved along theI-beam and can be secured to the I-beam 53 so that there can be norelative motion therebetween. The clamping member 54 is adapted to besecured to a vehicle chassis such as shown at 55.

By clamping the vehicle chassis 55 to the frames 51, 34 and 35 it isensured that the transducer apparatus 47 measures only movement of thewheel 32 relative to the vehicle chassis 55 as permitted by thesuspension arrangement SE acting between the vehicle wheel and thevehicle chassis. Furthermore the clamping of the chassis 55 to theframes ensures that all forces are reacted within the frames andtherefore the frames need not be secured in a substantial manner to thefloor beneath them.

Whilst the drawing does not show a transducer arrangement connected tothe wheel 33, such an arrangement will in fact be used and alsoactuators will be provided to cause motion of the wheel support means 31in a similar fashion to the means provided for the wheel support means30.

FIG. 3 shows a third embodiment of the invention which is simpler thanthe two previous embodiments and only has actuators which can applyforces longitudinally along and transversely of the vehicle. Theembodiment comprises two wheel support means 60 and 61 which are mountedon top of reaction plates 62 and 63. Each reaction plate has legs 64which allows the reaction plate to be adjusted relative to the floorbeneath to ensure that the reaction plate lies in a horizontal plane.

A frame 65 is provided which comprises two transverse I-beam members 66and 67 with two longitudinal members 68 and 69 connected therebetween.Each transverse member has two upright members 70 which each haveclamping means 71 provided thereon for securing the vehicle chassis 72so that it cannot move relative to the frame 65.

The two longitudinal members 68 and 69 respectively have upright flanges73 and 74. A mechanical actuator 75 of the ball and screw type isprovided between the upright flange 73 and the wheel support means 60and a mechanical actuator 76 is provided between the upright flange 74and the wheel support means 61. The actuator 76 is also of themechanical ball and screw type. The actuators 75 and 76 can be used toapply transverse forces on the support means 60 and 61 and/or displacethe support means 60 and 61 transversely.

Upright flanges 82 and 84 are provided on the transverse member 66. Amechanical actuator 83 is provided to act between the flange 82 and thesupport means 60 and an actuator 85 is provided to act between theflange 84 and the support means 61. The actuators 82 and 85 can be usedto apply longitudinal forces on the support means 60 and 61 and/ordisplace the support means 60 and 61 Longitudinally.

Two frames 77 and 78 are provided transversely distanced from the frame65 and positioned to align with the wheel 79 and 30. The frames 77 and78 are secured to the surface below them.

In the FIG. 3 wheel transducer apparatus 81 can be seen acting betweenthe frame 77 and the vehicle wheel 79, to enable measurement of theposition of the wheel 79. This transducer apparatus will be described inmore detail later on. A similar transducer apparatus will be providedbetween the frame 78 and the wheel 80, although it is not shown in thefigure.

FIG. 4 shows an embodiment of wheel support means according to theinvention. This wheel support means has been previously shown in theembodiments of FIGS. 1, 2 and 3. The wheel support means comprises wheelplate 90 which is connected to a bearing mounting plate 92 by four forcetransducers, two of which are seen at 94 and 95. The four forcetransducers can be seen with reference to the plan view shown in FIG. 5at 91, 93, 94 and 95. The bearing mounting plate is supported on airbearings 96 which react on reaction plate 97.

Typically nine air bearings 96 are provided for each bearing plate 91.The construction of each of the air bearings 96 will be described ingreater detail with reference to later figures.

Two actuators 98 and 99 are shown schematically in FIG. 4.

In FIG. 5 the actuators 99 and 98 can again be seen and the actuator 99can be seen to comprise also a force transducer 100. A similar forcetransducer will be provided for the actuator 98, although this is notshown.

In FIG. 5 it can be seen that the actuators 98 and 99 act at the centrepoint of the vehicle wheel support means.

FIG. 6 shows a detail of an air bearing as used in embodiments of theinvention shown in FIGS. 2, 4 and 5. The air bearing comprises a lockingmember 110 a washer 111, a series of three belville springs 112, 112,114 and a ball bearing 115 which allows movement between a bearingmember 116 and tie air bearing plate 117.

The bearing mounting plate 92 is secured to the bearing member 116 bylocking member 110. The bellville springs 112, 113 and 114 act betweenthe bearing member 116 and the bearing mounting plate 92, via the washer111.

Further locking members 116 and 119 are provided to limit the motion ofthe bearing member 116 relative to the air bearing plate 117. The ballbearing 115 allows relative motion between the bearing member 116 andthe bearing plate 117.

The bearing plate 117 has running through it a series of air passages,such as shown as 120. A series of air nozzles such as 121 and 122 allowair to flow from the air passage 120 to the outside of the air bearingplate 117. An air inlet 123 is provided connected to the air passage120.

Typically the air nozzles such as 121 and 120 are 0.2 mm in diameter andtypically nine nozzles are provided for each bearing plate which istypically 150 mm².

A plan view at an air bearing plate can be seen in FIG. 7 and a thirdelevation view of an air bearing plate can be shown in FIG. 8.

The vehicle suspension testing apparatus of FIG. 1 can have air bearingswhich comprise only a bearing plate having air passages and nozzles anddoes not require the bellville springs or ball bearing arrangement. Thevehicle suspension testing apparatus shown in FIG. 1 is adapted forlighter weight vehicles and only requires three air bearings for eachsupport means to achieve required lift. A tripod arrangement of thethree air bearings will ensure even load distribution and adequate liftbetween all points of the support means and the surface below. However,the embodiments of FIGS. 2 and 2 are adapted to cope with heavy vehiclesand will typically have nine air bearings for each support means toensure adequate lifting force. In such cases it is advantageous toinclude the bellville springs and ball bearings in the arrangementdescribed above to allow the support means to align with the surfacebelow it and to ensure even load distribution and adequate lift at allpoints.

FIG. 9 shows how the actuators 99 and 98 are secured to the wheel plate90 and the bearing mounting plate 92. A locking member 130 is providedwith a threaded portion 131 at its lower end. The locking member 130secures the wheel plates 90 to the bearing mounting plates 92.Sandwiched between the wheel plate 90 and the bearing plate 92 are twospacer members 132 and 133 and two rose joints 134 and 135. The twospacer members 132 and 133 are located respectively adjacent the wheelplate 90 and the bearing mounting plate 92, with the two rose joints 134and 135 located therebetween.

The actuator 98 is connected to the rose joint 134 which itselfcomprises two members 136 and 137. The actuator 98 is connected to themember 136 which is located around the inner member 137. This canclearly be seen in FIG. 10 which is a cutaway view of the wheel plate90.

The inner surface of the member 136 is rounded and matches the roundedexterior surface of the inner member 137. The matching surfaces allowpivoting of the member 136 relative to the member 137, whilst securingone member relative to the other. It is clear that the joint allows freepivoting of both wheel ptate 90 and bearino mounting plate 92 relativeto the actuators 98 and 99.

Transducer apparatus according to the invention can be seen in FIG. 11.The transducer apparatus comprises a frame 140 which can be secured tothe surface below it and takes the form of a square or rectangularvertical upright frame located on two feet members 142 and 143 withreinforcing diagonal members 144 and 145 acting therebetween.

A cylindrical rod member 146 extends downwardly from the top portion ofthe upright frame 141. A sleeve 147 is positioned on the downwardlyextending rod 146 and can be secured relative to the rod by a clampingmember in the form of a threaded rod extending through the sleeve 147which is turned to engage the rod 146 by an arm 148.

Extending from the sleeve 147 are two arms 149 and 150. At the outermostends of the arms 149 and 150 two sensor arms 151 and 152 are pivotallyattached to the arms 149 and 150. Each sensor arm 151, 152 has Y-shapedportions at both ends. The Y-shaped portions of each arm have aperturesrunning therethrough and the two arms 151 and 152 are pivotally securedto the arms 150 and 149 by locking members running through the aperturesof the Y-shaped portions at first ends of the sensor arms. The Y-shapedportions at the second ends of the sensor arms 150 and 151 are rotatablerelative to the Y-shaped portions at the first ends of the sensor armsabout the centre lines of the sensor arms 150 and 151.

Two wishbone members 153 and 154 are pivotally attached to the ends ofthe sensor arms 151 and 152 such that they can pivot relative to thesensor arms in one sense only.

The wishbone members 153 and 154 are also pivotally mounted at theirother ends to a wheel clamping member 155 such that the wishbones 154and 153 can only pivot relative to the wheel clamping member 155 in onesense only.

The wheel clamping member 155 has means 158 provided thereon to enablethe wheel clamping member to be secured either to the centre of avehicle wheel or to the rim of a vehicle wheel.

A cable 156 is secured to the point of pivotal attachment to thewishbone member 154 and the wheel clamping member 155. The cable 156 islooped around a spool 157 which is pivotally mounted to the sensor arm152 to be rotatable about an axis coincident with a pivot axis of thewishbone 153.

The sensor arms 151 152, as mentioned before, can rotate about a pivotaxis running through the arms 149, 150. The rotation cit the sensor armsis sensed by sensors 160 and 161 which measure together the toe andtrack of the vehicle wheel.

As mentioned above, the sensor arms 151 and 152 each have one end whichis rotatable relative to the other end about an axis running through thearm. Such rotation is measured by a sensor 162 which measures thevertical displacement of the wheel.

The cable 156 and the spool 157 together define part of a stringpotentiometer from which fore and aft movement of the wheel can bemeasured.

A sensor 163 is provided on the wheel clamping member 155 and thismember is a gravity referenced inclinometer which measures the camber ofthe vehicle wheel.

A further gravity referenced inclinometer 164 is provided on theclamping means 156 and this measures the castor of the vehicle wheels.

The sensors are preferably connected to a computer system whichprocesses the signals to display motion of the vehicle wheel on a VDUscreen.

The transducer arrangement can typically provide the followingmeasurements;

1. Vertical Displacement (Z)

2. Lateral Displacement (X)

3. Fore-Aft Displacements (Y)

4. Steer Displacement (TOE) Angle

5. Fore Canner Change

6. Wheel flotation

7. Roll Centre Height

8. Roll stiffness

9. Self-Aligning stiffness

10. Vertical Force on the Wheel

11. Lateral Force on the Wheel

12. Fore-Aft Force on the Wheel

A modification of the embodiment of FIG. 3 can be seen in FIG. 14. Fortesting purposes the vehicle wheel is removed and a jacking assembly 200is provided. This enables vertical movement to applied on the wheel hub.

The jacking apparatus 200 comprises a frame 201 wich supports a verticaljacking actuator 202. The top of the vertical jacking actuator isconnected to a gimble mounting assembly which is adapted to be connectedto the wheel hub. The gimble assembly allows 25° of axle articulation.

The frame 201 is provided at its lower end with air bearings 203, aspreviously described. Transducer apparatus 206 is provided to measurethe movement of the wheel hub under loading.

Preferably the actuator 202 is a precision ground linear ball screwactuator powered by a variable speed DC motor. This enables simple andcheap actuation with a high degree of accuracy and the ability tomeasure displacment directly from the actuator.

Use of the apparatus previously described and a method of testingvehicle suspension system will now be discussed with reference to FIGS.12 and 13.

A commercial passenger vehicle 170 is driven up ramps 171 and 172 suchthat one of the vehicle wheels 173 is located on suspension testingapparatus according to the invention. Although in FIG. 11 only one wheelis located on suspension tasting apparatus, it is envisaged that bothvehicle wheels 173 and 174 could at the same time be located onsuspension testing apparatus and this will be clearly seen from theearlier figures of the application in which testing apparatus isprovided in parallel for two wheels. The wheel 173 is located centrallyon the wheel support means 175. It is envisaged that the wheel plate ofthe wheel support means will have marked thereon a locating spot for thevehicle wheel which would typically DC a square on the top of the wheelplate. The wheel is located such that the centre of the hub liescentrally in the plate or such that the centre of the of hub is distantslightly forward (in the sense of vehicle motion) of the centre of theplate, to allow for "pneumatic trail".

When the vehicle is in motion, the actual point on the tyre throughwhich force is transmitted to the vehicle road does not lie directlybeneath the wheel hub, due to the deformation of the tyre under rollingmotion. Instead, when a vehicle is moving forward, the force istransmitted at a point behind the centre of the vehicle hub at adistance which is defined as the "pneumatic trail" of the tyre. Thepneumatic trail for a particular tyre is evaluated by vehicle tyremanufacturers and is supplied with technical details for the tyre.

Since it is important to measure characteristics of a suspension in use,it is preferable to locate the wheel on the plate such that pneumatictrail is taken into account.

The wheel 173 can be located by simply measuring the position of thewheel 173 from the edges of the wheel plate.

Once the vehicle 170 is located on the suspension testing apparatus 175the vehicle 170 is secured relative to the testing apparatus by clampingthe vehicle chassis to the frame of the vehicle testing apparatus.

The vehicle 170 is preferably bolted to the test rig frame at its normalride height, so that the force in the wheel plates is representative ofnormal reaction of the wheel.

By securing the front section of the vehicle to the test rig framework,the forces generated during a test are reacted within the test rigstructure and this eliminates the need for a strong floor installation.

Once the vehicle body 170 has been secured then loads are applied to thevehicle wheel 173 by the actuators of the suspension testing apparatus.For instance, if apparatus according to FIG. 3 is used then themechanical ball screw actuator 83 would be used to apply a forcelongitudinally of the vehicle, the mechanical ball screw actuator 75would be used to apply a force laterally of the vehicle.

The actuators used are preferably precision ground linear ball screwmechanisms which are powered by variable speed high performance electricmotors. The arrangement allows a quiet reliable low maintenance means ofcontrolling load applications.

The air bearing plate of the wheel support means will in use beconnected to a supply of pressurised air, typically at 90 psi.

The air bearing arrangement permits low noise movement of the wheelplate with negligible friction. The air bearings generate considerablyless friction than mechanical bearings and this is a crucial factor tothe accuracy of a suspension test rig, particularly when largecommercial vehicles are used of considerable weight, since obviously thefriction generated is proportional to the force on the wheel supportmeans.

It is important to ensure that the wheel plate lies in a horizontalplane when in use and to enable this the air bearings comprise thespring and ball bearing arrangements previously discussed. Each springallows a small amount of vertical motion, while the ball seat allows thewheel plate to align against the reaction plate. Such deformation andalignment ensures that the wheel plate remains in a plane parallel tothe plane surface below and ensures that the load is transmitted equallythrough all of the air bearings.

The lift of the air plate when the pump is working varies between 0.05and 0.08 mm. It is important to provide the springs and bearings toallow alignment of the air plate with its reaction surface, since it isvery difficult to machine a plate uniformly flat over its surface andtherefore there needs to be the facility for some adjustment to accountfor undulations in the surface of the plate.

The system will automatically allow the plate to align itself with itsreaction surface to ensure that there is lift between both.

Various tests can be carried out on the suspension. For instance, thecharacteristics of the suspension under braking can be determined bylocking the wheel tested and applying a force longitudinally along thevehicle using an actuator such as 83.

Transducer apparatus such as previously described will be connected tothe wheel 173 and will measure the displacement of the wheel 173 whenthe force is applied thereto to record the linear translation androtation of the wheel. The measurement of the transducers can then beused to evaluate the suspension kinomatic and compliance deflectioncharacteristics.

When initially attaching the transducer apparatus to the wheel it ispreferable to ensure that the four corner angles of the apparatus, i.e.the angles between the wishbone members and the sensor arms and thewheel mounting member, are all 90°.

As well as the forces and the deflections noted by the transducerapparatus, the force transducers between the wheel plate and the bearingplate of the wheel support means of FIGS. 2, 3, 4 and 5 or the earcetransducer 21 of FIG. 1 also note the vertical tarce on the wheel.

The use of four force transducers in the apparatus of FIGS. 2, 3, 4 andS between the wheel plate and the cearing plate ensures that the forcetransducers together always weigh the net vertical force on the wheelplate.

As mentioned above, the ball and screw actuators used give a directmeasurement of displacement of the support means.

The construction of the preferred embodiment of the invention ensuresthat both lateral and longitudinal forces are applied to the centre ofthe wheel plate of the support means, whilst allowing free rotation ofthe plate, thereby allowing free movement of the wheel when the force isapplied. It is very important to apply forces at the centre of the wheelplate since this ensures that the point of application of the force doesnot change with wheel rotation. If the point of application or forcechanges during wheel rotation then this has to be taken into accountwhen calculating the vehicle suspension deflection characteristics underloading, since, for instance, a lateral force can apply a rotationalcouple on the wheel it the point of appitcation of the force is awayfrom the pivot axis of the rotation. This can easily happen, forinstance, if the actuator acts on the exterior of the wheel plate ratherthan acting at the centre of the wheel plate.

As mentioned above, it may not be desirable to locate the centre of thewheel hub directly above the centre of the plate, since the tester maywish take into account pneumatic trail, which has been discussed above.This pneumatic trail can be typically be in the range of 40 to 55 mm andthe wheel can be accordingly offset from the centre of the plate, toensure that force is applied to wheel at the point in the tyre throughwhich load is usually transmitted.

With apparatus as shown In FIGS. 1 and 2, vertical force can be appliedon the vehicle wheel and this is a more sophisticated system than thesystem of FIG. 3 which can only apply lateral and longitudinal forces orthe vehicle wheel However, the arrangement of FIG. 14 could be usedsubsequently to the arrangement of FIG. 3, to allow testing of asuspension under vertical loading.

To mimick exactly the motion of a wheel on braking it may be desirableto increase the vertical reaction on the wheel to account for thetransfer of weight between the wheels at the vehicle on braking. This ispossible with the embodiments of FIG. 1 and 2.

As mentioned above, the actuators are preferably precision ground linearball screw mechanisms powered by variable speed electric motors. Thedisplacement of the actuators can be controlled by a computer tosimulate forces on the wheel during braking. These linear ball screwsare generally very accurate and are for instance accurate to 0.5 mm over300 mm extension. They also enable the easy measurement of displacement,since the revolutions of the ball screw can be counted to determinedisplacement.

As can be seen in the FIGS. 10 and 11 the rear wheels of the vehicle arepreferably jacked up using standard jacking equipment. The workingsurface of the wheel plate will typically be 350 mm above the groundplane and the rear of the vehicle will be raised accordingly.

In a preferred embodiment an additional transducer can be provided tomeasure chassis deflection relative to the frame of the suspensiontesting apparatus during the loading. Obviously, it is desirable tomeasure only the movement of the wheel relative to the chassis and notthe movement of the chassis relative to its surroundings. By measuringchassis deflection it is possible to subtract any such deflection fromthe recorded deflection of the wheel to arrive at an accuratemeasurement of the load/deflection characteristic of the suspensionarrangement.

The apparatus of FIGS. 1, 2 and 14 is adapted a measure "bump steer".When a vehicle is travelling around a corner and encounters a bump thenthe steering angle of the wheel can vary with the bump. The apparatuscan be used to measure change in steer angle with suspension movementfor roughly 50 mm of movement, so that kinematics of the linkage can bedetermined.

Obviously the apparatus shown in FIGS. 1 and 2 can be used for bumpsteer measurement, since they incorporate vertically acting actuators.The embodiment of FIG. 14 is intended as an additional feature of thesimplified apparatus of FIG. 3, which does not normally possess avertical actuator.

When conducting bump steer tests on large vehicles with leaf springs itmay be necessary to remove several leafs from the leaf spring assemblyto leave a single leaf.

The use of a single leaf will enable determination of deflectioncharacteristics of the suspension during loading enabling use of astandard actuator, which would have difficulty in supplying sufficientforce to a multi-leaf suspension arrangement.

The arrangements of FIGS. 3 and 12 can be used on a standard workshopfloor with the minimum of installation requirement, although aninspection pit can be advantageous.

Whilst in FIGS. 12 and 13 the vehicle suspension apparatus is shown inuse tasting a commercial passenger vehicle the apparatus and method ofthe invention can be used to test any vehicle of any size haivng asuspension system.

To conclude, the invention provides in one aspect a suspension testingapparatus which is very accurate since it uses air bearings which have avery low coefficient of friction which is typically five times less thanthe coefficient of friction of mechanical bearings. This is especiallyimportant when the suspension systems of large vehicles are beingtested, especially since the weight of the large vehicles can lead toconsiderable frictional forces.

The invention provides in a second aspect suspension testing apparatuswhich ensures accurate measurement of suspension characteristics sincethe apparatus applies forces directly below the centre of the vehiclewheel hub (or forwardly or rearwardly therefrom at a distance equivalentto the pneumatic trail of the tyre in the wheel) to ensure that thepoint of application of a farce remains constant despite rotation of thesupport means for the wheel during deflection of the vehicle wheel.Otherwise the longitudinal and transverse actuators can apply rotationalforces on the vehicle wheel, leading to inaccuracies in measurement orleading to complications in the computing of accurate suspensioncharacteristics.

The invention in a third aspect provides new sensor means for measuringthe vehicle wheel deflection which uses a minimum number of transducersto accurately monitor tyre and wheel deflection during use.

The invention provides in a fourth aspect testing apparatus which usesmechanical actuators rather than hydraulic actuators to cause motion ofthe support means, which give an indication of the displacement of thesupport means. Such actuators are cheap, simple and precise. They arealso inherently safe since they remain in position until movement isrequired.

In a sixth aspect the invention provides a method of testing a vehiclesuspension using the apparatus of the invention.

I claim:
 1. Vehicle suspension testing apparatus comprising:wheelsupport means for supporting thereon a vehicle wheel, actuator means forapplying force to the wheel support mean in at least two directionsselected from the group of directions vertical to, transverse to, andlongitudinally along the vehicle, and sensor means for measuring thedisplacement of the vehicle wheel, wherein the actuator means isconnected to the wheel support means by pivotal connection meansdirectly below the center of the vehicle wheel, said pivotal connectionmeans allowing free pivotal motion of the wheel support means in atleast one plane.
 2. Vehicle suspension testing apparatus as claimed inclaim 1wherein the wheel support means comprises air bearing means whichin use raises the wheel support means above the surface therebelow andwherein the wheel hub support means has a flat lower exterior surfaceand the air bearings means comprises a plurality of air bearingsattached to the flat lower exterior surface of the wheel support meansby attachment means which allows limited motion of the air bearingsrelative to the flat lower exterior surface of the wheel support meansand which comprises spring means acting between the said flat lowerexterior surface of the wheel support means and the air bearings. 3.Vehicle suspension testing apparatus as claimed in claim 1 wherein thewheel support means comprises a wheel plate for receiving thereon avehicle wheel, the connection means is connected to the wheel supportmeans directly underneath the center of the wheel plate and the freepivotal motion allowed by the connection means allows the wheel plate torotate in the plane thereof.
 4. Vehicle suspension testing apparatus asclaimed in claim 1wherein the sensor means comprises a frame fixedrelative to the wheel, and a wishbone arrangement comprising first andsecond spaced apart arms each pivotally attached to both the frame andwheel clamp member attachable to the vehicle wheel, rotation sensorsbeing provided to measure pivoting of the first and second spaced apartarms relative to the frame and inclinometers being provided on the wheelclamp member to measure inclination thereof.
 5. Vehicle suspensiontesting apparatus as claimed in claim 1wherein the actuator meanscomprises a first mechanical actuator for moving the wheel support meansin a direction longitudinally along the vehicle and a second mechanicalactuator for moving the wheel support means transversely of the vehicle,which first and second mechanical actuators are respectively adapted toprovide indications of the longitudinal and transverse displacements ofthe wheel support means.
 6. Vehicle suspension testing apparatus asclaimed in claim 5 wherein the actuator means comprises additionallythird mechanical actuator for moving the wheel support means vertically,which third mechanical actuator is adapted to provide and indication ofthe vertical displacement of the wheel support means.
 7. Vehiclesuspension testing apparatus as claimed in claim 5 wherein themechanical actuators are all ball and screw type actuators.
 8. Vehiclesuspension testing apparatus as claimed in claim 7 where the ball andscrew type actuators are coupled to and are driven by electric motors.9. A method of testing a vehicle suspension system of a vehicleincluding the steps of:locating a wheel of the vehicle on the wheelsupport means of vehicle suspension testing apparatus claimed in claim1, attaching the sensor means to the vehicle wheel, applying a force tothe wheel support means using the actuator means, measuring force on thevehicle wheel using the sensor means.
 10. Vehicle suspension testingapparatus as claimed in claim 1 comprising additionally a frame on whichare mounted the wheel support means and the actuator means, saidactuator means acting between the frame and the wheel support means,said frame having a clamping means for securing the frame to the body ofthe vehicle being tested.
 11. Vehicle suspension testing apparatus asclaimed in claim 1 wherein the actuator means can apply a force on thewheel longitudinally and transversely of the vehicle.
 12. Vehiclesuspension testing apparatus as claimed in claim 11 wherein the actuatormeans can also apply a vertical forces on the wheel.
 13. Vehiclesuspension testing apparatus as claimed in claim 1 wherein the wheelsupport means comprises a wheel plate for receiving thereon a vehiclewheel and a bearing mounting plate located parallel to and verticallyspaced below the wheel plate to which air bearings are attached, theactuator means extending between the wheel plate and the bearingmounting plate to attachment means which attaches the actuator means tothe wheel plate and the bearing mounting plate respectively below andabove the centers of the plates, the attachment means allowing pivotalmotion of the plates, while restraining translational motion. 14.Vehicle suspension testing apparatus comprising:wheel support means forsupporting thereon a vehicle wheel, actuator means for displacing thewheel support means, and sensor means for measuring the displacement ofthe vehicle wheel,wherein the actuator means is connected to the wheelsupport means by pivotal connection means directly below the center ofthe wheel, said pivotal connection means allowing free pivotal motion ofthe wheel support means in at least one plane.
 15. Vehicle suspensiontesting apparatus as claimed in claim 14wherein the wheel support meanscomprises air bearing means which in use raises the wheel support meansabove the surface therebelow, and wherein the wheel hub support meanshas a flat lower exterior surface and the air bearings means comprises aplurality of air bearings attached to the flat lower exterior surface ofthe wheel support means by attachment means wich allows limited motionof the air bearings relative to the flat lower exterior surface of thewheel support means and which comprises spring means acting between thesaid flat lower exterior surface of the wheel support means and the airbearings.
 16. Vehicle suspension testing apparatus as claimed in claim14wherein the actuator means comprises a first mechanical actuator formoving the vehicle wheel hub support means in a direction longitudinallyalong the vehicle and a second mechanical actuator for moving thevehicle wheel hub support means transversely of the vehicle, which firstand second mechanical actuators are respectively adapted to provideindications of the longitudinal and transverse displacements of thevehicle wheel hub support means.
 17. Vehicle suspension testingapparatus as claimed in claim 16 wherein the actuator means comprisesadditionally a third mechanical actuator for moving the vehicle wheelhub support means vertically.
 18. Vehicle suspension testing apparatuscomprising:wheel support means for supporting thereon a vehicle wheel,having an axis of rotation and a tire thereon with a pneumatic trail,actuator means for displacing the wheel support means, and sensor meansfor measuring the displacement of the vehicle wheel, wherein theactuator means is connected to the wheel support means by below thevehicle wheel by pivotal connection means at a point on the wheelsupport means spaced from a plane containing the axis of rotation of thewheel by a distance corresponding to the pneumatic trail of the tire onthe vehicle wheel, said pivotal connection means allowing free pivotalmotion of the wheel support means in at least one plane.
 19. Vehiclesuspension testing apparatus as claimed in claim 18wherein the wheel hubsupport means comprises air bearing means which in use raises the wheelhub support means above the surface therebelow, and the wheel hubsupport means has a flat lower exterior surface and the air bearingsmeans comprises a plurality of air bearings attached to the flat lowerexterior surface of the wheel hub support means by attachment meanswhich allows limited motion of the air bearings relative to the flatlower exterior surface of the wheel hub support means and whichcomprises spring means acting between the said flat lower exteriorsurface of the wheel hub support means and the air bearings.
 20. Vehiclesuspension testing apparatus as claimed in claim 18wherein the sensormeans comprises a frame fixed relative to the vehicle wheel hub and awishbone arrangement for comprising first and second vertical spacedarms each pivotally attached to both the frame and wheel clamp memberfor attached to the vehicle wheel hub, rotation sensors being providedto measure pivoting of the first and second spaced apart arms relativeto the frame and inclinometers being provided on the wheel clamp memberto measure inclination thereof.
 21. Vehicle suspension testing apparatusas claimed in claim 18wherein the actuator means comprises a firstmechanical actuator for moving the wheel support means in a directionlongitudinally along the vehicle and a second mechanical actuator formoving the wheel support means transversely of the vehicle, which firstand second mechanical actuators are respectively adapted to provideindications of the longitudinal and transverse displacements of thewheel support means.
 22. Vehicle suspension testing apparatus as claimedin claim 21 wherein the actuator means comprises additionally a thirdmechanical actuator for moving the wheel support means vertically. 23.Vehicle suspension testing apparatus comprising:wheel support means forsupporting thereon a vehicle wheel hub, actuator means for applyingforce to the wheel hub support means, and sensor means for measuring theforce on the vehicle wheel hub,wherein the actuator means is connectedto the wheel support means by pivotal connection means directly belowthe center of the vehicle wheel hub, said pivotal connection meansallowing free pivotal motion of the wheel support means.
 24. Vehiclesuspension testing apparatus as claimed in claim 23,wherein the wheelhub support means comprises air bearing means which in use raises thewheel hub support means above the surface therebelow, and the wheel hubsupport means has a flat lower exterior surface and the air bearingsmeans comprises a plurality of air bearings attached to the flat lowerexterior surface of the wheel hub support means by attachment meanswhich allows limited motion of the air bearings relative to the flatlower exterior surface of the wheel hub support means and whichcomprises spring means acting between the said flat lower exteriorsurface of the wheel hub support means and the air bearings.
 25. Vehiclesuspension testing apparatus as claimed in claim 23wherein the sensormeans comprises a frame fixed relative to the vehicle wheel hub and awishbone arrangement comprising first and second vertical spaced armseach pivotally attached to both the frame and wheel clamp member forattachable to the vehicle wheel hub, rotation sensors being provided tomeasure pivot of the first and second vertical spaced arms relative tothe frame and inclinometers being provided on the wheel clamp member tomeasure inclination thereof.
 26. Vehicle suspension testing apparatus asclaimed in claim 23wherein the actuator means comprises a firstmechanical actuator for moving the vehicle wheel hub support means in adirection longitudinally along the vehicle and a second mechanicalactuator for moving the vehicle wheel hub support means transversely ofthe vehicle, which first and second mechanical actuators arerespectively adapted to provide indications of the longitudinal andtransverse displacements of the vehicle wheel hub support means. 27.Vehicle suspension testing apparatus as claimed in claim 26 wherein theactuator means comprises additionally a third mechanical actuator formoving the vehicle wheel hub support means vertically.
 28. Vehiclesuspension testing apparatus comprising:wheel hub support means forsupporting thereon a vehicle wheel hub, actuator means for displacingthe wheel hub support means, and sensor means for measuring displacementof the vehicle wheel hub, wherein the actuator means is connected to thewheel support means by pivotal connection means directly below thecenter of the wheel hub, said pivotal connection means allowing freepivotal motion of the wheel support means in at least one plane. 29.Vehicle suspension testing apparatus as claimed in claim 28wherein thesensor means comprises a frame fixed relative to the vehicle wheel and awishbone arrangement comprising first and second spaced arms eachpivotally attached to both the frame and wheel clamp member forattachable to the vehicle wheel, rotation sensors being provided tomeasure pivot of the first and second vertical spaced arms relative tothe frame and inclinometers being provided on the wheel clamp member tomeasure inclination thereof.
 30. Vehicle suspension testing apparatuscomprising:wheel support means for supporting thereon a vehicle wheelhaving an axis of rotation and a tire thereon with a pneumatic trail,actuator means for supplying a force to the wheel support means, andsensor means for measuring the force on the vehicle wheel, wherein theactuator means is connected to the wheel support means below the vehiclewheel by connector means at a point wheel support means spaced from aplane containing the axis of the rotation of the wheel by a distancecorresponding to the pneumatic trail of the tire of the wheel, saidconnection means allowing free pivotal motion of the wheel support meansin at least one plane.